Assembly and comparative analysis of the complete mitochondrial genome of Salix wilsonii using PacBio HiFi sequencing

Abstract

<i>Salix</i> L. (willows) is one of the most taxonomically complex genera of flowering plants, including shrubs, tall trees, bushes, and prostrate plants. Despite the high species diversity, only five mitochondrial genomes (mitogenomes) have been released in this genus. <i>Salix wilsonii</i> is an important ornamental and economic willow tree in section <i>Wilsonia</i> of the genus <i>Salix</i>. In this study, the <i>S. wilsonii</i> mitogenome was assembled into a typical circular structure with a size of 711,456 bp using PacBio HiFi sequencing. A total of 58 genes were annotated in the <i>S. wilsonii</i> mitogenome, including 33 protein-coding genes (PCGs), 22 tRNAs, and 3 rRNAs. In the <i>S. wilsonii</i> mitogenome, four genes (<i>mttB</i>, <i>nad3</i>, <i>nad4</i>, and <i>sdh4</i>) were found to play important roles in its evolution through selection pressure analysis. Collinearity analysis of six <i>Salix</i> mitogenomes revealed high structural variability. To determine the evolutionary position of <i>S. wilsonii</i>, we conducted a phylogenetic analysis of the mitogenomes of <i>S. wilsonii</i> and 12 other species in the order Malpighiales. Results strongly supported the segregation of <i>S. wilsonii</i> and other five <i>Salix</i> species with 100% bootstrap support. The comparative analysis of the <i>S. wilsonii</i> mitogenome not only sheds light on the functional and structural features of <i>S. wilsonii</i> but also provides essential information for genetic studies of the genus <i>Salix</i>.